Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Always less than unity

Any one of the above

Equal to unity

2. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Collect vapours

3. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.376

0.67

0.6

4. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Ericson

Carnot

Stirling

5. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

Takes place at constant entropy

6. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

7. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

8. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

High risibility with oil

Low boiling point

Large latent heat

9. Freon group of refrigerants are

Toxic

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

10. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

8 bar

30 bar

2 bar

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11. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

12. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

3.33

4.33

2.33

13. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

15°C

10°C

14. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Freon

Brine

Carbon dioxide

15. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

16. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Four heat exchangers

Three heat exchangers

17. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Miniature sealed unit

Axial

Centrifugal

18. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

19. Rating of a domestic refrigerator is of the order of

40 tons

5 tons

10 tons

0.1 ton

20. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

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21. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Condenser tubes

Capillary tubes

Refrigerant cooling tubes

22. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

23. The capillary tube, as an expansion device, is used in

Room air conditioners

Domestic refrigerators

All of these

Water coolers

24. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

25. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Positive

Negative

None of these

26. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Reversed Carnot

Carnot

27. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

28. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

29. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

30. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-56.6°C

-77.7°C

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31. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

32. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

33. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 3

1: 9

9: 1

34. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Compressor and condenser

Evaporator and compressor

Condenser and receiver

35. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

None of these

Normal cooling

36. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

37. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

38. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

39. For obtaining high COP, the pressure range of compressor should be

Low

Optimum

High

Any value

40. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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